Just a suggestion I've got is that you might want to increase the unbreaking level on some of the higher donor tools, especially pickaxes. At that high of a level of efficiency they'll instantly mine through anything except obsidian and some other stuff (analogous to netherrack with efficiency IV, sand with an efficiency V shovel, etc.) and if one isn't paying attention to their hotbar actively as they mine they could have pickaxes breaking in 10-15 seconds of mining, especially with double and triple drops due to the mcmmo plugin. Otherwise looks like an excellent idea :p
More ranks - to add more diversity would be fun.. Such as regular prison, has 4 basic letter ranks, free, then about 5 more impossible ranks :p It'd be cool if there was a wide-range, .. One of my favorite parts of prison , is ranking up.. It's sometimes hard to see the milestone, when you have so much ahead of you.. Please consider - Thanks.